In an ordinary loom setup, hundreds of warp yarns or threads pass from a supply into the weaving zone in side-by-side parallel relationship to one another. Each of the yarns passes through some shedding means such as a heddle eye, and during each cycle of loom operation, some of the warp yarns are displaced from others by the shedding means so as to form what is known as a "shed" through which one or more weft yarns may be inserted in a transverse direction.
A loom reed is interposed between the warp yarn shedding means and the place where the weft yarn is inserted. This reed extends across the entire width of the loom and is made up of a large number of thin vertical strips called "dents" regularly spaced apart from one another so as to leave spaces through which the warp yarns may pass without being prevented from making the vertical movements required in the formation of the shed. After a weft yarn has been inserted in a shed in front of the reed, the reed is moved forwardly to shift the inserted weft thread and accomplish a beatup action so as to position the new weft thread at the fell of the cloth being woven.
This sequence of operations is repeated over and over again as more and more weft threads are inserted and beaten up into the newly formed fabric.
It is crucial to quality weaving that the warp yarns be properly oriented with respect to the reed. Each warp yarn must occupy its proper space between selected reed dents, and the structure must be such that the warp threads are not damaged as a result of relative movements between such yarns and the reed parts. Moreover, the front edges of the reed dents must cooperate properly with the newly inserted weft threads in order to accomplish satisfactory beatup operations that will not lead to appearance defects (e.g. lines) in the woven fabric.
The one-by-one threading of the warp yarns through the spaces between the dents of the reed is an operation which is referred to as "drawing-in" or "reeding". It must be carried out whenever the particular loom is to be changed over to the production of a new fabric having a different thread setup, such for example, as different arrangements of warp thread colors and/or sizes and/or materials. The demands of fashion tend to increase the number of occasions for such changeovers.
Drawing-in operations also may be necessitated by accidents (e.g., "smash" events) which break or damage large numbers of the warp yarns. For instance, a misaligned shuttle may be lead to rupture of many of the warp threads. When this occurs, weaving cannot be resumed until the damaged warp threads have been again threaded through the proper spaces between the dents of the reed and newly tied into the fabric being woven.
Drawing-in operations can be carried out entirely by hand. For fine fabrics, such operations can be very tedious indeed, and mistakes lead to much lost weaving capacity. Yet, hand operations were the only practically available ones prior to the present invention for addressing situations which required drawing-in without removing the reed from the loom or otherwise disturbing the loom setup.
U.S. Pat. No. 2,707,317 proposes a drawing-in machine adapted to be clamped on top of a loom reed and having rails along which certain of the components may be moved in an effort to position them for reed threading operations. The disclosed construction utilizes a camming action derived from the threading instrumentality itself as motive force for stepwise movements intended to position the parts properly for successive threading operations. This approach is considered inadequate from a practical standpoint and incapable of yielding the precise control that is necessary in reed drawing-in operations.
There are available large machines to which a reed (separated from the loom) may be brought for reeding. Some of these have been proposed also for movement into positions adjacent looms, so that the loom reeds might be associated therewith and subjected to drawing-in by the mechanisms of the reeding machine.
These large machines are cumbersome to use and do not offer the flexibility often needed in weaving mills. Substantial amounts of setup time ordinarily are required in connection with their use. Moreover, problems have been experienced with regard to the maintenance of perfect registry between the drawing-in elements of these machines and the spaces between the reed dents. Typically, the drawing-in elements are moved in stepwise fashion across the reed, stopping in front of each dent-to-dent space to draw a warp yarn through such space. However, slight errors in the length of the advancing movement of the drawing-in elements tend to be cumulative as the elements move through the hundreds of cycles ordinarily required for threading a reed, so that occasions may arise when the threading instrumentalities or elements are not properly oriented with respect to a space between adjacent reed dents. On such occasions, there are risks of damage to reed parts and/or yarns as well as risk of improper threading of the reed.